Open Session - SWISS GEOSCIENCE MEETINGs

12.1
COLTOP 3D: A software dedicated to analyze relief using large DEM and
massive 3D-imaging cloud points
Metzger Richard, Jaboyedoff Michel & Oppikofer Thierry
Institute of Geomatics and Risk Analysis , University of Lausanne, 1015 Lausanne (richard.metzger@unil.ch)
The increasing precision of ground-based Lidar technologies makes possible to perform more detailed systematic structural
and morphological analyses than ever reached before. Using the orientation of each single collected vertex, a point cloud
data set can be represented by a 3D image where each single point has a color defined by the local dip and strike direction,
which allows a very simple slope analysis. This can also be applied to any surface reconstructed through the data set, making
the detection of planar structures within a cliff, i.e. in the presence of overhangs, possible, which is not with classical 2D
digital elevation models. Such simple analyses applied to 3D clouds of points make it possible to quickly identify structural
features affecting topography. They open new perspectives in relief analysis. This paper describes the basis (kernel) of a software
(Coltop-3D) which is dedicated to perform these tasks.
More specifically, the paper will focus on:
1. data organisation and management, as terrestrial laser scanners allow for capturing dense 3-dimensionnal data set (up to
millions of points) on the surface of an object, within a few minuts. Without such organisation , the post-treatment and
the standard operating use of such large data set may impair an in-depth analysis for specific applications, such as landslide
and rockfall analysis.
2. dip and strike direction estimation from raw data points. Numerous work have pinpointed that eigenanalysis of the covariance
matrix of a local neighborhood can be used to estimate local surface properties, and hence the normal. Once the
normal is known, it is straightforward to compute the dip and strike direction. Moreover, it will be shown that eigenanalysis
may be used to semi-automatically remove folliage from data sets.
A case study (Hegguraksla cliff site, located in the Norway) will also be presented.
12.20
A GIS approach for tsunami risk assessment
Monia Molinari*, Massimiliano Cannata*
*Institute of Earth Sciences – SUPSI, Trevano, C.P 72, CH-6952 Canobbio
The tragic event of Sumatra brought to the international attention a natural phenomenon that is well known by most inhabitants
of coastal areas: the tsunami. During the event of the 26th December 2004, a series of unusual high waves, up to 15
m, hit the coastal regions of Indonesia, Sri-Lanka, India, Thailand, Bangladesh, Maldives, Somalia and Kenya causing over
230˙000 victims.
Although these natural disasters cannot be avoided, their effects, such fatalities or damage to property, can be reduced
through preventive and adequate protection measures. With respect to this goal the availability of flood risk maps would
certainly help to foster the development of mitigation measures.
For this reason a procedure that enable GIS users to conduct tsunami risk assessment by means of a series of GRASS scripts
that implement the approach proposed in Federici et al. (2006) and validated in Cannata et al. (2007) was created.
This procedure allows to assess the maximum vertical height of the tsunami wave at the coast (run-up) and the subsequent
inundation on the mainland. The procedure takes into account local morphological characteristics, vegetation and urbanization
through the usage of a digital terrain model, landuse, and cadastre map.
This presentation illustrates the procedure through a case study located in Olbia, a Mediterranean city on the Sardinia
island's east coast.
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Symposium 12: Data acquisition, Geo-processing, GIS, digital mapping and 3D visualisation